The present invention relates to a method for the catalyzed synthesis of partially halogenated, fluorine-containing organic compounds with regeneration of the catalyst used.
It has long been known that fluorine-containing organic compounds can be synthesized by a halogen-fluorine exchange or by the addition of hydrogen fluoride using hydrogen fluoride in the presence of a catalyst. U.S. Pat. No. 2,005,710 discloses the synthesis of many alkanes containing fluorine, chlorine and optionally hydrogen. Antimony halide catalysts are described as preferred. If a pentavalent catalyst is reduced to the trivalent form, it is desirable that free halogen, such as chlorine, be present during the reaction or added at an arbitrary time (see column 13, lines 32 to 37 of U.S. Pat. No. 2,005,710). This method of regenerating the catalyst in fluorination processes using hydrogen fluoride is described in U.S. Pat. No. 2,510,872 as the state of the art which is to be improved. In the method described in U.S. Pat. No. 2,510,872, antimony pentafluoride is used. However, it is used there not as a catalyst, but as a fluorinating agent.
It has now proved possible to establish that the presence of elemental halogen, such as chlorine, is disadvantageous for the purpose of regenerating the reduced catalyst in the reactor when organic compounds are present which react with the halogen in an undesirable manner, for example, with elemental chlorine with the addition of the chlorine.